1. Field of the Invention
The present invention generally relates to devices and methods for removing tissue from body passageways and, more particularly, to a control system for a rotational and or orbital angioplasty device.
2. Brief Description of Related Developments
There are a number of different techniques and devices which have been developed for use in removal and/or repair of arteries and other similar body passages. One objective of some of the aforementioned devices and techniques is removal of atherosclerotic plaques from patient's arteries. Atherosclerosis is characterized by buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational angioplasty procedures are a common technique for removing such stenotic material. Such procedures are used most frequently to commence the opening of calcified lesions in coronary arteries. Often the rotational angioplasty procedure is not used alone, but is followed by a balloon angioplasty procedure. This, in turn, may frequently be followed by placement of a stent to assist in keeping the artery open. For noncalcified lesions, balloon angioplasty most often is used alone to open the artery, with stents often placed to maintain the opened artery. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience in-stent restenosis (i.e., blockage of the stent) which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. Rotational angioplasty devices were utilized in removing the excessive scar tissue from the stents and, thereby were useful in providing assistance in restoring the patency of the arteries.
It should be understood that rotational angioplasty devices and rotational angioplasty procedures are often referred to as rotational atherectomy devices and rotational atherectomy procedures. These terms may be used interchangeably herein.
One example of a rotational angioplasty device is shown in U.S. Pat. No. 4,990,134 (issued to Auth), wherein a front or distal portion of a burr is covered with an abrasive cutting material such as diamond particles. The diamond coated burr is mounted at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 140,000-180,000 rpm) while it is advanced across the stenosis. The burr has a solid cross-section and thus, as the burr is removing stenotic tissue, it blocks blood flow through the artery. Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. A series of different size burrs may be utilized to open the artery to a desired diameter. U.S. Pat. No. 5,897,566 (issued to Shturman) shows another rotational angioplasty device having a drive shaft made from helically wound wires. A section of the drive shaft has an enlarged diameter. In one embodiment at least a front or distal segment of this enlarged diameter section is covered with an abrasive material to define an abrasive segment of the drive shaft. The enlarged diameter section is hollow. This Shturman Device of the '566 patent is capable of opening an artery only to a diameter about equal to the maximum diameter of the enlarged diameter section of the drive shaft, thereby providing results similar to the Auth Device of the '134 patent. The Shturman Device of the '566 patent possesses certain advantages over the Auth Device of the '134 patent because it is more flexible. Another example of a rotational angioplasty device is provided in U.S. Pat. No. 6,132,444 (issued to Shturman et al.) describes a rotational atherectomy device having a flexible, elongated, rotatable drive shaft with an eccentric enlarged diameter section. At least part of the eccentric enlarged diameter section has a tissue removing surface with an abrasive surface to define a tissue removing segment of the drive shaft. When placed within an artery against stenotic tissue and rotated at sufficiently high speeds (e.g. in the range of about 40,000 rpm to about 200,000 rpm) the eccentric nature of the enlarged diameter section of the drive shaft causes such section to rotate in such a fashion as to open the stenotic lesion to a diameter substantially larger than the maximum diameter of the enlarged diameter section. Preferably the eccentric enlarged diameter section of the drive shaft has a center of mass spaced radially from the rotational axis of the drive shaft, facilitating the ability of the device to open the stenotic lesion to a diameter substantially larger than the maximum diameter of the enlarged diameter section. A drive shaft having an eccentric enlarged diameter tissue removal section with a diameter of not more than 2 mm is capable of opening stenotic lesions to a diameter equal to the original diameter of the coronary arteries (i.e., to a diameter of more than 3 mm) so that in a significant percentage of cases balloon angioplasty may not be needed to complete the procedure. The device is particularly useful for cleaning out partially blocked stents.
U.S. Pat. No. 5,314,407 to Auth, which is incorporated herein by reference in its entirety, shows the details of a type of an advancer (handle) that may be used in conjunction with rotational atherectomy devices of the type described in Auth '134 patent and Shturman '566 and '444 patents. A handle of the type shown in Auth '407 patent has been commercialized by Heart Technology, Inc. (Redmond, Wash.), now owned by Boston Scientific Corporation (Natick, Mass.), in the rotational atherectomy (angioplasty) device sold under the trademark Rotablator.RTM.
FIG. 1 is an illustration of a rotational angioplasty system 100 of the prior art. As shown in FIG. 1, the prior art system comprises a rotational angioplasty device 104, a fluid supply 106, a gas supply 108, a controller 102 and a foot pedal device 110.
The rotational angioplasty device 104 comprises an advancer assembly 134 that is located within a body or handle 136. A gas driven turbine (not shown) is located within the advancer assembly 134 and rotates a flexible, hollow drive shaft 138. An ablative, diamond coated burr 140 is attached at the distal end of the flexible drive shaft 138. The flexible drive shaft 138 together with the burr 140 may be rotated over a guide wire 141.
As shown in FIG. 1, a flexible sheath 142 extends distally from the handle 136 and surrounds the flexible drive shaft 138 substantially along its entire length.
The advancer assembly 134 also carries a water (saline) pump (not shown). This water pump is located distally to the gas turbine and has a shaft that is connected to the turbine shaft. The output of the fluid pump is in fluid connection with the lumen formed between the flexible drive shaft 138 and the flexible sheath 142.
The rotational angioplasty system 100 shown in FIG. 1 includes an infusion bag 128 to administer a saline solution. The saline bag 128 is pressurized with a pressure cuff 129 to ensure a steady supply of saline to the water pump within the advancer assembly 134 and around the drive shaft 138. The rotation of the gas turbine rotates the fluid pump and increases the fluid flow rate in a lumen between the flexible drive shaft 138 and the sheath 142. The fluid flow rate in this system depends on the rotational speed of the gas turbine. Thus, the fluid acceleration in the lumen between the drive shaft 138 and the sheath 142 can only take place simultaneously with the increase in rotational speed of the gas turbine, and the system can not increase the fluid flow rate in the lumen between the drive shaft 138 and the sheath 142 without increasing the rotational speed of the gas turbine.
A certain amount of static pressure must be applied and maintained against the saline bag 128 in order to provide an adequate fluid flow rate in the lumen between the drive shaft 138 and the sheath 142. This requires repeated repressurization of the pressure cuff 129 disposed around the saline bag 128.
The controller 102 has a front panel 112 that includes a power switch 113, a turbine control knob 114 (adjusts turbine pressure and RPMs), a turbine pressure gauge 115, a turbine (pneumatic) connector 116, a DynaGlide™. (pneumatic) connector 117, and a pair of fiber optic connectors 120. The front panel 112 also includes an event timer 122, a procedure timer 123, and an optical tachometer display 124. The optical tachometer provides or registers information about the rotational speed of the gas turbine of the rotational angioplasty device 104.
The foot pedal 110 is used as an on/off control for the gas turbine of the rotational angioplasty device 104. A DynaGlide™ button 126 is located on the right side of the foot pedal housing 132 and is used as an on/off control for the DynaGlide™ mode of operation.